Agnano & the Grotto
of the Dog —or, Now I know why I
couldn't find the Lake.

Mark
Twain, adding himself to the long list of travelers to
write about the infamous Grotto of the Dog, said this (in
The
Innocents Abroad):

Nero’s Baths, the
ruins of Baiae, the Temple of Serapis; Cumae, where
the Cumaean Sibyl interpreted the oracles, the Lake
Agnano, with its ancient submerged city still visible
far down in the depths — these and a hundred
other points of interest we examined with critical
imbecility, but the Grotto of the Dog claimed our
chief attention, because we had heard and read so much
about it. Everybody has written about the Grotto del
Cane and its poisonous vapors, from Pliny down to
Smith, and every tourist has held a dog over its floor
by the legs to test the capabilities of the place. The
dog dies in a minute and a half — a
chicken instantly...I longed to see this grotto. I
resolved to take a dog and hold him myself; suffocate
him a little, and time him; suffocate him some more,
and then finish him. We reached the grotto about three
in the afternoon...But now, an important difficulty
presented itself. We had no dog.

I was sure when I read
that passage that MT was wrong about the lake. There were
many points of Greek and Roman interest in the area, yes,
but there was no
Lake Agnano! Hmph!
Sage of Hannibal, indeed. I was outraged and triumphant at
the same time! Oops...(speaking of critical imbeciles), I
missed it by a century and a bit, but at the time MT was
there, there was indeed a Lake Agnano. It was drained in
1870, a short time after he passed through. It was not one
of the myth-shrouded lakes of ancient times (such as Lake
Averno) but had been around only since about 1100 AD when
seismic shenanigans created it in the middle of the Agnano
basin. The Agnano basin is on the eastern side of the Campi Flegrei, the volcanic
remnants of the event that produced the great Archiflegrean caldera collapse
about 40,000 years ago. The area shown in the above
map is about 30 km across. The Archiflegrean caldera is
the area bounded by the red lines with wedges. The Agnano
basin is labelled "Agnano." The lake filled much of the
basin. The Grotto of the Dog is about where the letter o is in the word Agnano. (There is now
a large and very popular horse-racing track right above
the word Agnano!)
(paragraph below
added, Nov. 2014)
What the Agnano basin was like before the lake formed in
the 11th century is speculative. The following is
excerpted (with permission) from The Ancient Thermal
Baths of Agnano & the Grotto of the Dog by
Selene Salvi of Napoli Underground (NUg). The entire
article is on the NUg website at
this link.

The Agnano
basin is the oldest crater from the third eruptive
period of the Flegrean Fields (8,000-3,900 years
ago)...The circumference of the basin is 6.5 km.
Since antiquity this site has been most commonly
sought after because of its therapeutic value-that
is, the presence of secondary volcanic phenomena
(thermal springs, fumaroles and solfatare-i.e.
sulfur vents). On the slopes of Mt. Spina you can
see the ruins of Roman thermal baths dated to the
1st-2nd century AD. They consist of an apodyterium,
a frigidarium, warm rooms (tepidaria, calidaria
and laconica) as well as a series of
interconnected cisterns. The complex was a
way-station for those on the roadbetween Neapolis
and Puteoli [Pozzuoli]; it was fed by the Serino
aqueduct of Augustus, using, as well, the
on-site underground hot-water springs...One theory
is that the [Grotto of the Dog] was hollowed out to
serve primarily as a steam room or thermal bath in
the 3rd-2nd century BC, at which time the infamous
gas had not yet broken into the chamber or at least
was somehow kept from building up within
it...Another fascinating theory connects the grotto
to those buildings from the Hellenic age of the
4th-3rd century BC found in the basin after the
draining and land reclamation (1870): the ancient
city submerged in the depths of a lake, the waters
of which had had such a harmful effect on travellers
over the centuries...

Measurements
of the lake before was it drained showed it to be
circular, 924,000 sq. meters (about 230 acres) in area,
and 12-15 meters/36-45 feet deep in the middle. By the
time of the draining, the lake had swamped up and turned
into a vast snake- and frog-infested, foreboding place.
Drying up the lake/swamp was part of land reclamation in
the south by the new Italy, united in 1861. The initial
work was done between 1865-70 and produced a fan-like
network of narrow channels of varying length covering the
basin (the lake bottom) (image, right). The channels
converged and, aided by a series of pumps, moved the lake
waters to the central hub (quaintly named "Fount of
Apollo"!) and into a drain tunnel through Monte Spina to
Bagnoli, two km away, and into the sea. The lake dried up
and revealed for the first time in almost a thousand
years, the large number of thermal springs, the
therapeutic value of which was known in ancient times.
But, indeed, the many tales over the last few centuries
from travelers who visited a noxious dog-killing cave on
the shores of a lake in Agnano are accurate. It is worth emphasis that the work in 1870
was not a one-time affair. It was the beginning of a
long-term project to reclaim land and manage water
resources in the area. (Indeed, if they stopped managing
and reclaiming, you'd wind up with another lake in no
time!) New canals and drains were added over the decades,
and in 1934 the Consortium for the Reclamation of the
Agnano Basin was set up to oversee and continue work.
Quite recently (2003) that consortium was expanded to
include "...and the Flegrean Basins" for a total area of
some 5,600 hectares (about 20 sq. miles). Indeed, today
you can stroll along the channels of the Agnano basin and
watch the dark, mineral-laden waters still wending their
way towards the Fount of Apollo. (One such channel is
shown in the photo, below on the right.)(The above map comes from Larry
Ray. His comments on his first impressions of this site
many years ago may be viewed here.)With
the draining of the lake in 1870, the many thermal springs
again became available, and for many years there has been
a spa, a thermal bath establishment, the Terme d'Agnano,
just below Mt. Spina at the southern end of the basin. The
Agnano baths were at their height of popularity in the
1920s; the hotel and baths were housed in one of the
grandest examples of Art Nouveau architecture in Naples
(photo, left), built in 1910/11 and designed by Giulio
Ulisse Arata. During WWII, the spa quartered the officers
and nurses of the US 21st General Hospital, which was
stationed there and at the nearby Mostra
d'Oltremare fairgrounds from December 1943 to
September, 1944; the building was demolished in 1961 and
replaced with the current facility, designed by Giulio De
Luca. The area degraded terribly after WWII and became an
eyesore from shoddy overbuilding and illegal waste
dumping. I drove by the baths hundreds of times over the
years and never knew about the lake, never knew that I was
100 yards from the Grotto of the Dog and never knew that I
was in the middle of an archaeological site that includes
Greek stonework and a Roman thermal bath complex. No
attention was paid to any of that by those who might have
done something about the situation.

That has changed. Over the past 10 years, various
private groups have remade the area. The grounds of the
Terme d'Agnano are pristine (photo, above left). On the
premises, there is a small section of stone put in place
by the Greeks (photo, above right) that has been explained
as part of the foundation of a retaining wall at the base
of Mt. Spina. There was probably a temple of sorts at that
spot and the whole site is thought to have been a rest
stop (and hot thermal bath!) at about the halfway point
for those moving between Neapolis and Cuma in around 300
BC. The stones are the only bit of ancient Greek masonry
in the Campi Flegrei.The
Romans, of course, enlarged the bath facilities
enormously. Their site here was explored partially in the
late 1800s and then documented by archaeologists in some
detail by 1911. The Romans honeycombed the entire northern
flank of Mt. Spina (now across the modern road from the
Terme d'Agnano) with a large thermal bath complex (photo,
left). It had warm rooms, hot rooms, cold rooms and
cisterns supplied by the main aqueduct that ran along the
top of Mt. Spina. (The aqueduct moved water to the Piscina Mirabilis and military port at Baia at the
western end of the gulf.) The cisterns also stored and
distributed thermal water from the natural on-site
springs. It's hard to say how the thermal springs and
baths fared during the dark ages following the fall of the
Roman Empire. (I don't imagine that Vandals and Goths took
a lot of baths, but I don't really know.) In any event,
the beneficial waters of the Agnano springs took a severe
blow in 1100 when the lake, itself, came into existence.
It swamped over in time and the area developed a very
unwholesome reputation. A 1775 map of the lake drawn by G.
Carafa Duca di Noja describes it as a lake with "...no
fish but countless frogs and entangled snakes that fall
into the waters and die, accounting for the
stench..." But the lake and shore have seen some service since
the middle ages; the same description says that Alfonso I
of Aragon (who ruled from 1442-58) used the waters of the
lake for the steeping (or retting) process in the
production of linen.

Visitors to the Grotto of the Dog
(the gate in the background, left.)

I said that the "many
tales...[about]...a dog-killing cave on the shores of a
lake in Agnano are accurate". Well, to a certain extent.
Drawings from the 1600s and 1700s idealize the lake—no
snakes or frogs! Many of them (such as the one at the top
of this page) show the entrance to the Grotto of the Dog
as adjacent to a thermal bath called the Le Terme di San Germano.
They're not really that near each other, but I suppose it
doesn't matter—Grand Tourists were allowed to liven up the
truth a bit. (And MT may have been right about the lake,
but, "...The Lake
Agnano with its ancient submerged city still visible far
down in the depths..." is stretching it a bit. He
and I have agreed to call it even.) The essentials are
that the grotto (that you may now see, photo, right) is
behind the Terme d'Agnano Hotel. The cave is about 10
meters long with steps leading down into it. The space
still fills with naturally occurring carbon dioxide from
the thermal vents and hugs the ground like fog (since it
is heavier than the surrounding air) in such
concentrations that you can see it from the entrance; it
really would knock tiny little Fido out (and possibly kill
him) while leaving Owner unharmed (because his moronic
head is some feet above the thick layer of CO2). But not
to worry, most paintings of the fun had by all (except the
dogs) show humans, yes, dragging doggies into the gas, but
then throwing them in the lake to revive them. The pooches
supposedly trotted out again, confused but alive.

This site was one of the 22 Royal
Bourbon properties in the Kingdom of Naples. They
range from the large Royal palaces to smaller
residences and hunting lodges. This is the
complete list with links to entries:

I repeat, many volunteers
(and that includes volunteer divers with special
masks!) are responsible for dredging and cleaning out the
grotto as well as for clearing away waste and vegetation
from the Roman site over the last few years. Among these
groups are the Association for the Agnano Basin, the
Naples Archaeology Group, the Speleological Research Unit
of the Civil Protection Center of Naples, and the Bagnoli
Hotel Training Institute. They worked in collaboration
with Terme d'Agnano, Inc. and the Special Superintendency
for Archaeology of Naples and Pompei. They continue to
work and lead tourists to the Greek stones, the Roman
baths and the Grotto of the Dog. The property of the Terme
d'Agnano, itself, the modern hotel and thermal bath
facility, extends for about 30 acres to the north and
northeast; the area contains 75 identified thermal springs
and is becoming increasingly more pleasant to visit. Bring
your own dog.